The present invention relates to a method of preserving cut flowers, wherein the cut flowers are placed with their stems into a holder, which holder is provided with a bottom and contains an aqueous gel as medium, and the gel is prepared by allowing granules of a water absorbent cross-linked polymer to swell.
It is known that to preserve cut flowers they generally have to stand substantially continuously in water. This also applies during transport, especially for the most delicate cut flowers such as lathyrus. During the transport of holders filled with water the water may splash out, or the holders may fall over so that the cut flowers stand dry. At the same time, bacteria and moulds and consequently diseases as, for example, botrytis may spread through the water. A further disadvantage is that the cut flowers have to be transported vertically, which means that more space is required. This in turn raises the transport costs. It makes transport of cut flowers over large distances very expensive.
To solve this problem the prior art proposes the use of a gel (see, for example, SE-8403211). The known gels exhibit various disadvantages. Some gels themselves serve as medium for bacteria, thereby increasing the problem of spreading of disease. The advantage of gels based on swollen granules is that if they inadvertently become distributed over plant parts, only a smaller cart will become infected compared with a gel based on a dissolved polymer. From practice and from literature the use of gels based on granules with a size of 0.5 mm is already known. The interstitial spaces between the swollen granules contain liquid water. This water is still able to spread diseases, albeit to a limit degree. For this reason is a known practice in the prior art to dissolve a polymer in said interstitial water and to mare the water into gel. Such a gel is relatively complex (different gel forming components) and has been shown in practice to be difficult to handle, for example, when transferring the gel into a holder. If a gel is used that has been prepared by adding to the granules only so much water as the granules are able to absorb, a cut flower that has been inserted into the gel will be unable to take up sufficient water.
It is the aim of the present invention to eliminate the above-mentioned disadvantages to a large extent.
To this end the method according to the present invention is characterized in that the stems are inserted into a gel on polyacrylamide basis, in which the size of the dry granules is 0.2 mm or smaller.
Surprisingly it has been shown that a gel based on a polyacrylamide-comprising polymer, in which the granules in dry condition have a size of 0.2 mm or smaller, is not only easier to handle (i.e. easier to pump), but also that there is no longer any need for a polymer in solution. Moreover, it appears that sufficient water is released for the preservation of the cut flowers. Without wishing to be bound to any theory, it is believed that due to their larger surface area smaller granules are better able to release water to be taken up by the cut flowers. The gel used in the method is liquid, that is to say it is able to flow. The lower-limit size of the granules does not appear to be typical, but preferably it will in general be larger than the diameter of the capillaries of the respective cut flower. Although a soluble polymer may be used, it is not required and by refraining from doing so, a simple gel-forming composition may be provided.
A gel suitable for application in the method according to the present invention contains sufficient gel-forming polymer to increase the viscosity of the aqueous medium such that it will not easily splash or run out of the holder. The upper limit of the concentration of gel-forming polymer in a gel according to the invention is determined by the ability of the gel to release water to the cut flower. With the method according to the present invention there is no objection to the gel exhibiting some syneresis, that is to say that it temporally loses water.
Depending on the desired flow behaviour and the storage life of the cut flowers, a person knowledgeable about gels is able in a simple manner to determine a suitable concentration of gel-forming polymer. If a higher concentration unacceptably shortens the storage life, the concentration of gel-forming polymer has to be reduced. If the aqueous medium is too thin, the concentration of gel-forming polymer has to be increased. Reference in the present application to a granule size of less than 0.2 mm is understood to mean a size distribution of granules, in which more than 80% by weight, and preferably at least 90% by weight of the granules have a size of 0.2 mm or smaller.
A typical suitable concentration of gel-forming polymer is 3 to 25 g per liter, and is preferably 5 to 20 g per liter of the final gel.
According to a preferred embodiment, the gel comprises 6 to 14 g gel-forming polymer per litre of the final gel.
According to a favourable embodiment the aqueous gel further comprises at least one compound chosen from the group comprised of a disinfectant, a surfactant, nutrients and a colouring agent.
The first three promote the storage life of the cut flowers. A colouring agent may, for example, be used for the identification of a gel with a particular composition, for example, to indicate for which kind of cut flowers the gel is suitable.
According to a very favourable embodiment the aqueous gel comprises polyacrylamide and has a pH between 2.5 and 7, preferably between 4 and 6.5.
Such gels have been proven to be very effective for the preservation of cut flowers.
The method according to the present invention is in particular also suitable for the reservation of cut flowers during transport. The cut flowers are preferably transported in a substantially horizontal position.
As a result it has become possible to also transport cut flowers that are sensitive to dryness using up a smaller volume. This means that air transport is more often economically feasible, thereby allowing the supply to markets that could previously not be catered for because of the short life that would remain for the flowers once they have reached the consumer. For nearer markets applies that the consumer is able to enjoy the flowers longer. The term xe2x80x9csubstantially horizontallyxe2x80x9d is understood to mean an angle smaller than approximately 25xc2x0.
The present invention also relates to a gel on water basis provided with nutrients for cut flowers, which gel has been prepared by allowing granules of a water-absorbent cross-linked polymer on polyacrylamide basis to swell, which granules in dry state have a size 0.2 mm or smaller.
Finally, the present invention relates to a holder for the preservation of cut flowers, which holder comprises a bottom and an opening for the insertion of the stem of the cut flower and is provided with a gel according to the invention, which holder is further provided with means for keeping the end of a stem of the cut flower at a distance from the bottom.
Especially when the stem of the cut flower has been cut straight across, there is a risk when using the gel according to the present invention that due to contact with the holder the cut-off end does not make sufficient contact with the gel granules, so that the cut flower does not receive an adequate amount of water. This is particularly a problem with the gel according to the present invention because of the smaller diameter of the water-conducting channels between the swollen gel granules (capillary forces). The provision of means for distancing ensures that sufficient gel granules make contact wit the cut end of the flower.
According to a preferred embodiment the holder is provided with sealing means chosen from the group comprising i) a cap sealing the opening by means of clamps; ii) pierceable membrane; and iii) a removable membrane provided with means for removing the membrane by pulling it off.
Such a holder can be prefabricated and can simply be prepared for use for the preservation of a cut flower by a flower grower, florist or consumer.